Abstract

Background

Circulating tumor cells (CTCs) are accepted as surrogate markers for tumor response and linked to shorter survival in castration-resistant prostate cancer (CRPC) patients. Thus, detection of CTCs has become an important addition to the clinical care toolbox. The only approved method, the CellSearch® prognostic kit, captures only epithelial cell adhesion molecule (EpCAM)-positive CTCs and suffers from low yield of CTCs and limited ability to perform molecular analysis. The CellSearch® profile kit also relies on EpCAM to enrich CTCs but integrates laser scanning cytometry (LSC) to perform molecular and genetic analysis of CTCs. This study compared CTC recovery by the CellSearch® prognostic kit and the CellSearch® profile kit in CRPC patients. We assessed the use of CTCs as a prognostic factor for clinical monitoring of CRPC patients in real time and evaluated the association between CTC number, laboratory and clinical characteristics, and overall survival (OS).

Table: 911P

CellSearch Prognostic*

CellSearch Profile + LSC

CTCs Enumerated

<5 CTCs

5-99 CTCs

>100 CTCs

<5 CTCs

5-99 CTCs

>100 CTCs

Patients Enumerated

19

3

1

7

8

9

Median (range)

0 (0-4)

42 (40-70)

-

0 (0-0)

37 (8-79)

209 (119-1314)

Patients Alive

14

0

0

2

6

7

Patients Dead

5

3

1

5

2

2

Median OS Range

13.05(12.82-21.2)

4.44 (0.89-6.25)

-

12.42 (0.89-13.05)

- (4.67-21.2)

- (2.63-9.87)

* - 1 N/A

Methods

CTCs were enumerated using the CellSearch® prognostic kit and the CellSearch® profile kit in 24 CRPC patients. A side by side comparison was performed on two 7.5 mL blood samples collected from each patient. Clinical variables included metastatic site(s) and number, Gleason score, PSA, CEA, chromogranin A, NSE, alkaline phosphatase, LDH, sedimentation rate, and C-reactive protein. The probability of patient survival over time was estimated by the Kaplan-Meier method.

Results

Overall, higher CTC counts were obtained by the CellSearch® profile kit and LSC method compared to the CellSearch® prognostic kit.

Conclusions

CTC enumeration by the integrated CellSearch® profile kit and LSC yielded improved CTC recovery compared to the standard method. CTC counts correlated with disease severity and support the use of CTCs as predictors of OS. We will present a comparison of CTC enumeration with a correlation to clinical variables.